This invention relates to roll-up type screens, and more particularly, to improvements in the take up mechanism used therein.
In the conventional roll up type screen, the screen is rolled onto a shaft housing a spring which is wound by pulling out the screen and which powers the rolling up of the screen, and uses a locking arrangement which depends on the force of gravity. An operator will pull out the screen and the locking mechanism, which usually has a ratchet and wheel arrangement, will cause the ratchet to lock into the wheel when the operator stops pulling and lets go.
However, disadvantageously, such locking arrangements are deficient in that first to lock, there must be a slight backing up of the roller until the ratchet catches, and second, to unlock, the screen must be pulled slightly and then released.
There is no braking arrangement in the prior art so that depending on the length at which the screen is pulled out, when rolling up different forces will be exerted on the screen, causing possible tearing. Also, at the outermost length, the spring force may be so great that the slight pulling necessary to release the ratchet may cause tearing of the screen. Furthermore, the spring will cause the screen to roll up in a burst of speed if the screen is released by the operator, since no braking arrangement is in the prior screens.